Method of concrete floor construction



Oct. 25, 1955 w. T. BURKE 2,721,369

METHOD OE CONCRETE FLOOR CONSTRUCTION Filed March 18, 1952 JNVE/vv-oe.wLLfA/v/ 7'. BURKE.

BKZ a i United States Patent Office 2,721,359 Patented Oct. 25, 1955METHOD OF CONCRETE FLOOR CONSTRUCTION William T. Burke, Pittsburgh, Pa.

Application March 18, 1952, Serial No. 277,307

1 Claim. (Cl. 25-155) This invention relates to concrete structures, andmore particularly to concrete oors and roofs, and has for one of itsobjects the provision of a concrete mixture of such composition that theresulting slab or the like will have greater strength for a given weightof material than various structures heretofore employed, wherebylighterweight steel framing and reinforcement may be employed inbuildings into which concrete enters than is possible with variousconcrete compositions heretofore employed.

Another object of my invention is to provide an irnproved method oflaying oors and the like, whereby concrete slabs and the finish coatingsor layers of concrete thereon will be more firmly bonded together thanheretofore.

Still another object of my invention is to provide a concrete mixture ofsuch nature that conduits and metal reinforcements and structuralmembers will be more intimately encompassed by the concrete, by reasonof the better flowability of the concrete mixture, even though a smalleramount of cement is incorporated thereon than is sometimes employed.

In ordinary steel frame structures, it is customary to lay conduits forelectric and telephone wires on top of the steel beams and over the topof the heavy concrete structural floor or roof slab, after which alight-weight concrete floor fill is disposed on top of the concretestructural slab and covering the conduits. Later, after the radiatorsare installed and the plastering done, a cement mortar floor finish isapplied to the fioor fill.

I propose to make the structural fioor or roof slab and the fill from alight-weight concrete of similar compositions. I also am able, in manycases, to eliminate the floor fill operation, by incorporating theconduits in a structural light-weight concrete slab, and I also make thecement mortar oor finish an integral part of the structural slab andprofit by the great compression value of the cement fioor finish.

In making the cement mortar floor finish, which is applied after thefloor fill and the structural slab have hardened, I use, in thestructural slab, and also in the fioor fill concrete, sharp-edgedvesicular surfaced aggregates which are derived from crushing suchmaterials as expanded slag, clay or shale, etc., and also coral, pumiceor crushed air-cooled blast furnace slag. The surfaces of theseaggregates are vesicular or pitted, and provide excellent anchorage forthe bonding of other concrete bodies to them. By making the concretefrom those aggregates and incorporating in the mix a relatively smallamount of water-cooled granulated slag and making this concrete of acertain plasticity, I find when I screed the body that the sharp-edgedaggregates tilt up and are left only partially buried in the mix, Theupper ends of the aggregates so displaced project above the body of theconcrete structural slab or fill. Furthermore, a void is left behindeach of the displaced aggregates and the fiuid cement in this body doesnot fill the void, so that numerous voids are left on the screededsurface and form excellent keyways to permanently anchor the cementmortar finish, and the up-ended or displaced aggregates project into thecement mortar oor finish and the sharp-edged and the vesicular surfacesthereof assist in securely and permanently anchoring or bonding thisfloor finish to the slab or fill. These displaced aggregates, beingfirmly embedded in the supporting slab and into the floor finish,guarantees that the finish layer is strongly bonded to the concretesupporting slab and can be taken into account when designing the slab.Rounded aggregates like gravel do not tilt to a substantial degree whenthe mix is screeded.

It has been customary to use a concrete, that is expanded by aluminumpowder, for this oor fill, but bonding permanently a cement mortar fioorfinish to this type of fill is expensive, as the surface has to becleaned and a coat of cement grout is brushed on the surface of thefill. Furthermore, expanded concrete is hard to handle in cold weatherand in hot weather and only certain brands of Portland cement reactsproperly to the aluminum powder expanding agent. Small gravel or gritsare used in this expanded concrete, and as they have round surfaces,they cannot be tilted like sharp edge aggregates.

Cinders were once common and were used extensively as an aggregate infloor fill concrete, but the advent of powdered coal, gas and oil forheating purposes have made cinders too scarce.

To make the supporting structural heavy-weight concrete slab and thefloor fill concrete from a common light-weight mixture would be anadvantage, as the two bodies would better unite, so that the concretefill instead of merely being a useless dead weight could go to work andhelp the support slab in shear and compression. By making these twobodies of one common material, I make more simple the mixing and supplysituation, and I greatly reduce the dead weight. For example, an oicebuilding steel beam supported concrete floor and fill by presentpractice have the following dead weights, based on approximately sevenfoot spans between supports. 51/2 inches heavy concrete structuralsupporting slab=66 lbs., 31/2 inches of expanded concrete=35 lbs., and linch finish=l2 lbs., all making a total dead weight of 113 lbs. persquare foot of fioor. The total thickness of the floor would be l0inches. Using light weight concrete whose aggregates have sharp-edgedand vesicular surfaces, I cast the structural slab and later integrallybond the concrete fill to it and later apply the cement mortar floorfinish. Using a light-weight concrete of 108 lbs. per cubic foot weightand having 2000 lbs. per square inch in ultimate compression, I canreduce the dead load as follows. With the same thickness of slab, whichis l0 inches, of which 9 inches is light-weight concrete, with a weightof 8l lbs. per square foot and allowing l2 lbs. per square foot for theweight of the finish, a total of 93 lbs. is obtained for the dead load.Thus, a saving of 20 lbs. per square foot is obtained. It may bepossible to reduce somewhat the total thickness of this oor. Thishomogeneous body could act as a fiat arch restrained by the spaced steelbeams and very little reinforcing steel would be required in the body.

Where the separate iioor fill operation can be avoided, then it ispossible to omit the floor fill dead weight and make the supporting slabfunction also as a conduitcovering body. In this case, the workmen inlaying the conduits can work on the temporary field forms which willsupport the floor slab, and after the laying of the conduits, the floorcan be completed in one operation, except for the finish which has to beapplied later; as experience has taught builders that it costs too muchto protect the iioor finish from damage by other mechanics in thebuilding, and it is better to wait until the ventilating, heating andplastering contractors are finished before finishing the oors. Thesaving in dead weight from making the structural slab function as theiill also is very great. For example, a total of only 6 inch thicknesswill be required for the slab, which at inches for the light-weightconcrete would be 45 lbs. per square foot and l2 lbs. per square footfor the finish would be a total dead load of only 57 lbs. per squarefoot, which is almost half the dead load required by present practice.

In the drawing, which more fully describes my invention, Figure l is afragmentary section of my concrete floor slab, including the lill; Fig.2 is a fragmentary section of my floor, till, and finish; Fig. 3 is afragmentary section of my combination floor slab and ll with finish, andFig. 4 is a sectional view showing a conventional form of structure, forpurpose of comparison with that of Figs. 2 and 3.

In Fig. l, I show an enlarged section of a concrete slab, wherein thebase or body portion 2 has coarse aggregates 3 which will be tiltedupright during screeding of the initial layer 2, so that not only willsuch aggregates frequently project slightly above the screeded surface,but whether or not they project above the screeded surface, there willbe voids left at 4, assuming that the screeding is done from right toleft in the example shown. Also, the surface at x is scarified somewhatby the rough screeding operation.

When the till layer 5 is applied, the material thereof will enter thevoids at 4 and thereby become keyed in the voids. Also, mortar in thefill 5 will enter the vesicular or pitted surface of the aggregates 3,and there will be good adherence to the rough surface at x.

For convenience of comparison, l use Fig. 4 which shows a sectionthrough a present type of structure that has a iioor 6 and steel beams 7that support a structural concrete slab 8 and conduits 9 that areembedded in expanded concrete 10 and cement mortar lioor finish 11.Reinforcement 12 is embedded in the slab S. The supporting slab 8 ismade from heavy concrete Weighing perhaps 150 lbs. per cubic foot, andits plaster coat 13 is very diflicult to apply and make permanently bondto this dense heavy concrete. There is here no bond between thestructural slab 8 and the lill 10, and poor bonding is obtained betweenthe iill 10 and the iinish 11.

In Fig. 2, I show a structural arrangement similar to that shown in Fig.4, except my structural slab 14, which is supported by a steel beam 15and contains reinforcing steel 16, is made from a light-weight concretemixture described above. In Fig. 2, a conduit 17 rests on a beam 15 andthe slab 14 and is covered by my floor lill 18 which is made of the samematerial as used in the slab 14. Floor fill 18 is bonded to slab 14 inthe same manner as shown in Fig. l, and the floor till 18 is bonded tofloor finish 19 also in the same manner as shown in Fig. 1. A plastercoat 20 bonds iirmly to my concrete mix, due to the vesicular surfacesof the aggregates. The bonding together of the structural slab, till andfinish makes a much stronger tioor membrane and provides better windbracing for the building.

Fig. 3 shows my combination iioor and fill slab 21 supported by steelbeams 22 and including reinforcing 23; the conduits 24 resting uponsteel beams 22 and on blocks 25' which, in turn, rest on a temporaryform 26. The slab 21 is bonded to floor finish 27 in the same fashionasdescribed in Fig. l. The mechanics who install the conduit can walk onthe form 26 and, as soon as the conduits are laid, the slab material 21can be applied. The great strength of the rich-in-cement floor finishhelps to compensate for some of the loss of cross section in the slab,where the conduits are located, but the conduits are almost always atthe neutral axis of the slab, and any reduction of area would not weakenthe slab. Raceways with outlets are generally run at right angles to thespaced supporting beams and do not cut across the compression area ofthe salb. The narrow width of these raceways would have little adverseeffect when positioned at right angles to the supporting beams.

A fuller description of the above described light weight concrete licorlill composition is outlined in my co-pending patent application, Ser.No. 277,306, tiled March 18, 1952.

As stated in said application, crushed air-cooled blast furnace slag isused in my light weight concrete composition, in combined sizes rangingfrom large sizes to small sizes, and l incorporate in the mix arelatively small amount of friable cellular granulated blast furnaceslag, adding a less than usual amount of Portland cement and water, andmixing this composition to a certain plasticity.

l claim as my invention:

The method of making a concrete body that comprises screeding a plasticconcrete slab that contains sharpcornered aggregates, while causing someof the aggregates to become tilted by the screeding tool, to effectprotrusion thereof from the surface of the slab, the remainder of themixture being of such plasticity that voids will remain behind thetilted aggregates, and thereafter applying a cementitous layer to thesaid surface of the slab, to ll the voids and imbed the protrudingaggregates.

References Cited in the tile of this patent UNITED STATES PATENTS Re.16,799 Burdge Nov. 29, 1927 829,293 Reilly Aug. 2l, 1906 1,573,896 AltonFeb. 23, 1926 1,707,055 Driscoll Mar. 26, 1929 1,740,336 Crittal et al.Dec. 17, 1929 2,268,311 Sheehan Dec. 30, 1941 OTHER REFERENCES Journalof the American Concrete Institute- April 1949, pages 582-583.

